Acetylcholinesterase: pivotal roles of its long omega loop (Cys69-Cys96) in regulating substrate binding.

Acetycholinesterase (AChE) hydrolyses neuronal and non-neuronal acetylcholine (ACh) very efficiently, and this possibly prevents the mitogenic action of ACh. AChE activity was measured in twenty-three samples of non-small lung carcinomas (NSLCs) and in their adjacent normal tissue. Twelve out of them were adenocarcinoma (AC), 6 squamous cell carcinoma (SCC) and 5 large cell carcinoma (LCC). The mean AChE activity in healthy lung was 10.95 +/- 6.90 mU/mg; in AC, 8.13 +/- 5.84 (p = 0.774); in LCC, 9.57 +/- 7.47 mU/mg (p = 0.063); and in SCC, 2.25 +/- 0.67 (p = 0.028). AChE dimers and monomers were identified in healthy and tumoral tissues and their contribution was not affected by cancer. The fraction of AChE molecules reacting with the lectin Con A increased in squamous cell carcinoma when compared to control, adenocarcinoma and large cell carcinoma specimens. The increased level of ACh in lung cancers, resulting from the fall of AChE activity, may collaborate to lung cancer growth.